Nano PHYSICS . MECHANICS . MOMENTUM AND COLLISIONS . CENTER-OF-MASS MOTION

Net External Force & COM Motion

The center of mass accelerates according to external forces only. Internal forces cancel in the system sum, so COM motion reveals the effect of the outside world on the whole system.

Physics · Mechanics · Momentum and Collisions · Center-of-Mass Motion · Net External Force & COM Motion
Access for this nano-lesson
Unsigned visitors can show & copy prompts for Steps 1-3. Signed-in free accounts can also Run with AI for Steps 1-2. Paid accounts unlock everything (Steps 1-6 + Help prompts + AI).
Steps 1-3 Free Steps 4-6 Paid
STEP 1
Orient: net external force & com motion
Free
Establish center-of-mass motion as the motion of a system's mass-weighted representative point.
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Goal: define COM motion using system choice, total mass, external force, and physical meaning.
STEP 2
Conceptual grounding: build the COM-motion model
Free
Build a workflow for systems, total mass, external force, internal forces, total momentum, and frame choice.
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Goal: distinguish individual-object motion from center-of-mass motion.
STEP 3
Real-world connection: interpret systems, frames, and relative motion
Free
Apply COM-motion reasoning to isolated systems, collisions, explosions, recoil, and reference-frame changes.
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Goal: explain isolated-system COM motion, COM-frame reasoning, collisions, explosions, and recoil in physical contexts.
STEP 4
Check your understanding: diagnostic mini-quiz
Paid
Attempt each question before revealing the COM-motion reasoning.
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Goal: identify and correct internal-force, external-force, recoil, frame, and collision-path errors before they become calculation errors.
STEP 5
Practice: solve increasingly rich COM-motion situations
Paid
Apply the model to situations that grow in complexity.
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Goal: write concise, physically justified COM-motion calculations and explanations.
STEP 6
Summary & reflection + explorations
Paid
Consolidate the model and explore changing external forces, systems, masses, velocities, frames, and recoil setups.
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🔒 ▶ Explore interactive simulation
Goal: carry the model forward into collisions, explosions, recoil, center-of-mass frames, and system momentum analysis.